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Hi Renato,</div>
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>> The largest part of that is enabling in-order scheduling using the Cortex-A55 schedule model. This is similar to the Arm backend change from eecb353d0e25ba which made -mcpu=generic perform inorder scheduling using the Cortex-A8 scheduling model.</div>
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> <span>I think this makes sense because the A55 scheduling model is more likely to benefit the chips produced nowadays than the A8's.</span></div>
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<span></span>Just to be explicit, eecb353d0e25ba was for the ARM backend, so AArch32, this is for AArch64. But I agree the ARM backend could benefit from an update too.
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> <span>Thinking out loud, what do people think of creating an additional "ooo" target? So, "generic" is the same as "in-order", but the "ooo" (or "unordered", whatever) would pick a base OOO target, like A57, A72, etc.</span><br>
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Sounds interesting!<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> on behalf of Renato Golin via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Sent:</b> 04 October 2021 10:08<br>
<b>To:</b> David Green <David.Green@arm.com><br>
<b>Cc:</b> llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> Re: [llvm-dev] [RFC][AArch64] Make -mcpu=generic schedule for an in-order core</font>
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<div dir="ltr">On Mon, 4 Oct 2021 at 08:43, David Green via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<br>
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Hello folks,<br>
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We would like to start pushing -mcpu=generic for AArch64 towards enabling a set of features that is believed to be beneficial in general - that improve performance the for some CPUs without hurting it on any others. A blend of the performance options hopefully
beneficial to all CPUs.<br>
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<div>Hi David,</div>
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<div>This is the usual LLVM definition of "generic", so working on that goal is always good.</div>
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The largest part of that is enabling in-order scheduling using the Cortex-A55 schedule model. This is similar to the Arm backend change from eecb353d0e25ba which made -mcpu=generic perform inorder scheduling using the Cortex-A8 scheduling model.<br>
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<div>I think this makes sense because the A55 scheduling model is more likely to benefit the chips produced nowadays than the A8's.</div>
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When specifying an Apple target, clang will set "-target-cpu apple-a7" on the command line, so should not be affected by this change when running from clang. This also doesn't enable more runtime unrolling like -mcpu=cortex-a55 does, only changing the schedule
used.</blockquote>
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<div>Thinking out loud, what do people think of creating an additional "ooo" target? So, "generic" is the same as "in-order", but the "ooo" (or "unordered", whatever) would pick a base OOO target, like A57, A72, etc.</div>
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<div>A few years ago, when I was doing benchmarks for OpenBLAS changes on Arm, I realised doing that was beneficial to most targets, often only beaten by specifying the correct target.</div>
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<div>cheers,</div>
<div>--renato</div>
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